1. Field of the Invention
The invention relates to microwave receiver/transmitter earth stations of the type having a reflector dish and, in particular, to low cost structures for such.
2. Prior Art
Microwave receiver/transmitters of the so-called reflector dish type have long been known in the communications industry. To date, most have been of industrial quality, namely--large, exceptionally ruggedly constructed units suitable for long-lived use in remote locations. Examples of such units are the relay stations installed by telephone companies. Units of this type cost one or more thousands of dollars. With the advent of communications satellites sited in geosynchronous or "parking" orbits some 22,300 miles above the earth's equator (in the so-called "Clarke Belt"), broadcasting of television and other signals from end to end of a continent or even from one continent to another with just one relay station (the satellite) has been made possible, but a high cost of the receivers--if it persists--would be a barrier to establishment of a market among the members of the general population. Further, the prior dishes have generally been heavy, ungainly and unsightly--particulary when formed of open framework--and (where non-uniformly exposed to the full strength of the sun's rays) have a tendency to warp, with resultant decrease in stability of the response characteristic to the input signals. This last has usually been taken care of by introduction of compensating electronic circuits with corresponding increase in actual cost of the item.
Use of plastic foams has long been known in conjunction with antennas in general and also with respect to those of the reflector dish type--e.g., patents such as U.S. Pat. Nos. 2,689,304; 3,169,311; 3,374,482; 3,381,371 and 3,745,158. The teachings in these patents relate to methods of making lightweight reflectors, embedment of a tilted reflector as a means of reducing dynamic unbalance of rotating radar scanners, combination of this last with a gyro rotor, and lastly, embedment of a double halo marine frequency antenna after separating the halos a predetermined distance by use of a number of spacers. Clearly, these patents do not address and solve the problems of supporting microwave receptor elements without deleterious effects of tripodal support arms on signal power and similarly undesirable effects of warping attendant upon non-uniform solar heating of the reflector dish. Moreover, none of these patents show embedment of electronic circuits along with the antenna elements because, as known, high heat dissipation of a-c/d-c power converters when combined with low thermal conductivity of plastic foam adversely affects active elements of these circuits, resulting in high probability of an early failure (thermal runaway).
Thus, there is need for a low cost, relatively light weight, compact, and yet thermally stable microwave earth station suitable for use in the mass market.